Semiconducting materials find uses in many applications. For example, semiconducting materials can be used in electronic devices as processors formed on semiconductor wafers. As a further example, semiconducting materials can be used to convert solar radiation into electrical energy through the photovoltaic effect.
The semiconducting properties of a semiconducting material may depend on the crystal structure of the material. Notably, faults within the crystal structure of a semiconducting material may diminish the material's semiconducting properties.
The grain size and shape distribution often play an important part in the performance of semiconducting devices where a larger and more uniform grain size is often desirable. For example, the electrical conductivity and efficiency of photovoltaic cells may be improved by increasing grain size and the uniformity of grains.
For silicon-based solar photovoltaic cells, the silicon can, for example, be formed as an unsupported sheet, or can be supported by forming the silicon on a substrate. Conventional methods for making unsupported and supported articles of semiconducting materials, such as silicon sheets, have several shortcomings. Methods of making unsupported, i.e., without an integral substrate, thin semiconducting material sheets may be slow or wasteful of the semiconducting material feedstock.
Methods by which unsupported single crystalline semiconducting materials are made include, for example, the Czochralski process, which may lead to significant kerf loss when the semiconducting material is sliced or cut into a thin sheets or wafers. Methods by which unsupported multicrystalline semiconducting materials are made include, for example, electromagnetic casting and ribbon growth techniques, which may be slow, producing about 1-2 cm/min for polycrystalline silicon ribbon growth technologies.
Other useful methods for producing unsupported multicrystalline semiconducting material are disclosed in U.S. Provisional Patent Application No. 61/067,679, filed Feb. 29, 2008, titled “METHOD OF MAKING AN UNSUPPORTED ARTICLE OF A PURE OR DOPED SEMICONDUCTING ELEMENT OR ALLOY,” the disclosure of which is hereby incorporated by reference.
Supported semiconducting material sheets may be made less expensively, but the thin semiconducting material sheet is limited to the substrate on which it is made, and the substrate has to meet various process and application requirements, which may be conflicting.
Thus, there is a long-felt need in the industry for a method to make unsupported articles of semiconducting materials, which method may improve crystal grain structure of the article of semiconducting material, reduce material waste, and/or increase the rate of production.